0003948: Other theme cannot be activated, and previous theme is corrupted, if there is sTheme option set in config.inc.php

Description

the Basic Theme cannot be activated in Community Edition Demo Shop

Steps To Reproduce

Currently you have Azure theme set as active on eShop.
- go to Admin -> Extensions -> Themes

- click on "Basic"

- click on "Activate"

... nothing happens, nothing changes.
But in frontend Azure theme now is also corrupted. And there is no possibility to set back to Azure (because it's still shown as "active" in Admin) to get back to correct stage.

How to reproduce:
1. Add to config file param $this->sTheme with same theme as in database.
2. Change theme in database.
If you change from azure to basic you get warnings instead off articles list in mine page.

Solution.
1. In all places should check only from one place: from database or from config file.
2. In admin there should be a warning that one couldn't change theme because it is in config file or that config param don't do nothing because of setting in database.

In next patch there will be an announcement that sTheme or sCustomTheme are in config file.
Still need to investigate possible fix for shop to work even if params are in config file and possible cases if there would be other params in config file.